There are well established techniques for testing deterioration of high voltage (HV) equipment, and specifically the insulators of that equipment. Such methods involve first disconnecting the equipment from the HV line. The purpose of disconnecting the equipment is to avoid the substantial danger to personnel and/or testing equipment that is connected to high power equipment. In practice, it has been very expensive to disconnect equipment for testing. In addition to the man-power required to disconnect the HV equipment, connect it to test equipment and perform the test, the service of the equipment is lost for whatever period of time it takes to disconnect, make the test and reconnect. If there are large numbers of transformers and circuit breakers, and other equipment to be tested, the shut-down can be lengthy and the loss of revenue to the power company very substantial.
Testing the condition of insulation in HV equipment is an essential task. The insulation which is most subject to deterioration is contained within the HV standoff insulator and includes oilpaper insulation and a metallic foil or, alternatively, a conductive coating on the paper wrapped in a roll around the HV conductor at the center of the insulator. The insulating oil which surrounds the transformer, or other HV device, within the grounded metallic casing extends into contact with and saturates the oilpaper to improve its insulation properties. Deterioration usually occurs in the paper or metal foil or coating. Age and temperature contribute to such deterioration, particularly hot spots which may ultimately burn the paper. The actual time of deterioration can vary considerably and, therefore many power companies adopt a schedule of offline testing. The standard testing for insulator deterioration is widely known as Power Factor or Tan/δ testing to determine when power factor of an insulator has reached a dangerous condition and the insulation should be replaced. Normal aging of HV equipment is a slow process that can take place over 30 to 40 years due to thermal, electrical and environmental effects. Premature failure on the other hand is often a relatively sudden process that is not anticipated by periodic off-line tests. Failure to detect insulation deterioration can result in disastrous consequences, ultimately causing heating of the equipment, fire and explosion. Heat may generate various hydrocarbon gases from the oil used in the transformer and some of these gases, such as acetylene, are highly flammable and may be explosive. Pressure builds up and gases are eventually ignited when fire occurs or heating becomes extremely severe so as to initiate a spontaneous combustion. The resulting explosion shatters porcelain insulators and sends pieces flying, damaging adjacent equipment. In a sub-station, or other areas where multiple sets of equipment are employed, an explosion not only results in loss of the exploded device, but also may result in damage to other very expensive equipment, as well as posing substantial danger to personnel working in the area, or even to passers-by in some locations.
The eventual breakdown of insulation is a rapid avalanche of failing dielectric layers. Damaged or deteriorated dielectric is associated with the following: 1) Increased dielectric losses (I2R) with other sources of heating may eventually fuel a mechanism of thermal runaway. PF is a measure of dielectric losses. 2) Partial discharges and treeing. High levels of partial discharge are reflected in the PF and are usually only present just after lightning or switching impulses and just before and during insulation failure. 3) Increased sensitivity to changes in temperature, humidity, and moisture (i.e., increased temperature coefficient). Sources of heating include dielectric losses, ambient temperature, and more significantly, load fluctuations. Most power companies are faced with the dilemma of taking equipment offline and testing it with consequent loss of revenue to the company, or, alternatively, leaving the equipment online without testing longer than it should be. The latter course allows damage to occur and take its toll. Therefore, there has existed for many years a need for a safe means of frequently periodically testing transformer and circuit-breaker bushing insulators without taking the equipment offline. The present invention is directed to such a means, which include a system and a process for testing the equipment and accumulating data about the condition of insulation without taking the equipment offline.